1. Field of the Invention
This invention relates to an aluminum alloy clad sheet used for an automobile heat exchanger. This invention also relates to its production method.
2. Description of the Related Art
In producing a tube for an automobile heat exchanger such as evaporator or condenser, an aluminum alloy brazing sheet (hereinafter also referred to as a clad sheet) is generally used for the production.
Various aluminum alloy clad sheets have been disclosed for such application, and an exemplary such clad sheet is an aluminum alloy clad sheet including a core layer including an aluminum alloy, a filler layer including an Al—Si-based alloy formed on one surface of the core layer, and a sacrificial anode material layer including an Al—Zn-based alloy formed on the other surface of the core layer. In this clad sheet, fatigue life (fatigue strength), corrosion resistance, erosion resistance, brazeability, and the like have been improved by limiting the composition of the core layer, the filler layer, and the sacrificial anode material (see, for example, Japanese Patent Application Laid-Open Nos. H8-60280, H9-95749, and 2004-17116).
Conventional clad sheet, however, suffered from the problems as described below.
The clad sheets described in Japanese Patent Application Laid-open Nos. H8-60280 and H 9-95749 had the problem that their use was difficult for a brazing tube in which the surface of the filler layer would be joined with the surface of the sacrificial layer since the sacrificial layer had magnesium added thereto. The clad sheet of Japanese Patent Application Laid-open No. 2004-17116 suffers from the risk of the loss of post-braze strength and the loss of fatigue life (fatigue strength) since average crystal grain size of the core layer after the brazing heat treatment is at least 300 μm.
In the automobile heat exchanger, attempts have been made to reduce the thickness of the clad sheet. However, further reduction in the thickness is strongly requested for reducing the weight, size, and cost of the heat exchanger. In order to reduce the thickness, the clad sheet should have an improved fatigue life and post-braze strength as well as high corrosion resistance and good erosion resistance, and brazeability.
While the level of the fatigue life, post-braze strength, corrosion resistance, erosion resistance, and brazeability has been improved in the conventional clad sheets, there is a demand for the development of a clad sheet having an even more improved fatigue life and post-braze strength and higher corrosion resistance as well as excellent erosion resistance and brazeability in order to realize the reduced thickness of the clad sheet.